Structured metal foils of this type are mainly used for catalysts and particle scrubbing devices in devices for the purification of exhaust gas.
It is known from prior art, for example, that a metal foil body made of corrugated and smooth layers of metal foil can be wound up, secured to one another, and attached to a cylindrical jacket that surrounds the winding body. Thus, depending on the nature of the surface structure of the individual layers and on the configuration of the adjacent metal foils, flow channels result through which the exhaust gas flows through the metal foil body. In most cases, the metal foils are coated with a coating that increases the specific surface or with a precious metal coating.
The metal foil bodies in the form of a winding body are preferably employed in the particle scrubbing devices used for the purification of exhaust gas in internal combustion engines for the deposition of carbon particles and as carriers for catalysts, in particular for gaseous emissions from diesel or gasoline engines.
When the metal foil body is used as a catalyst carrier, a conversion process for the purification of the exhaust gas takes place while the gases pass through the flow channels. By deflecting and turbulently mixing the exhaust gas, it is possible to increase the contact of the exhaust gas with the walls and the catalytically active coatings applied to said walls and required for the conversion process.
When the metal foils are used for the deposition of carbon particles, the deflection and the turbulence lead to a change in the direction and speed of the flow of the exhaust gas and, by means of diffusion and impaction, enable a removal of the particles from the flow and a deposition of the particles in the areas facing away from the flow.
For metal foils of this type, different surface structures and different configurations of the metal foils and combinations with smooth foils are used to ensure a suitable turbulence.
It is generally known from prior art that generic metal foils can be created in the form of corrugations or folds, with the creation of a varied surface topography by means of peaks and valleys which optionally also has openings.
The German Patent 20117873 U1 discloses a filter body for the purification of exhaust gas, which filter body is made of a foil with a structure which has elevations and troughs, with paddles being arranged in the elevations and troughs. The elevations and troughs are oriented in the longitudinal direction which runs parallel to the direction of the main flow, i.e., the corrugations run at right angles to the direction of the main flow. The paddles in combination with a paddle entry and a paddle exit form a passage for creating flow channels and enable the exhaust gas stream to pass over into adjacent layers of the filter body.
The German Patent 3744265 C2 describes a particulate filter for the purification of exhaust gas with a structure of the type described above, in which a layer of corrugated or pleated sheet steel and a layer of a plane filter material are alternatingly wound or stacked to form a winding body or package. In this case, the layer of corrugated or pleated material has a structure consisting of peaks and valleys that are alternatingly arranged side by side in the direction of the main flow and of joining strips that are arranged at a certain distance from one another at right angles to the direction of the main flow. These joining strips always run across the entire layer and at a constant height level. For joining strips that are located on the valley height level, there is a constant-height connection between the joining strip and the upstream and downstream valleys which are adjacent to said joining strip and which are arranged between the peaks in the direction of the main flow. By analogy, for joining strips that are located on the peak height level, there is a constant-height connection between the joining strip and the upstream and downstream peaks that are adjacent to said joining strip in the direction of the main flow. Thus, in the direction of the main flow, there are sections with a direct constant-height connection between the peaks and the valleys. The joining strips that run at right angles at the valley height level have only an insignificant effect on the change of the direction of flow and the flow velocity of the exhaust gas since the exhaust gas is not subjected to a direct forced deflection. Overall, there is little room for the deposition of particles since the cross section of the flow channel, both from the standpoint of the individual metal foil layers and from the standpoint of the entire body, contains only few zones of disturbance and, instead, has a relatively uniform contour. The greatest turbulence is achieved by a deflection [of the exhaust gas] into adjacent layers, which requires an extremely accurate placement of the layers with respect to one another so as to ensure a sufficiently large cross section for the passage [of the exhaust gas] into the adjacent layers. Overall, the flow channels that form promote a smooth flow and generate little turbulence since only few leading edges that deflect the flow are present; instead, said flow channels have sloped guide surfaces that give the flow a specific direction. As a result, this also leads to few “leeward” zones in which the flow is calmer, which is a prerequisite for the deposition [of particles].